The present invention relates to detachable couplings for surgical instruments. More particularly, the present invention relates to detachable couplings for attaching medical tools to various drive systems including handles to form surgical instruments, such as surgical instruments for facilitating total joint arthroplasty.
By way of background, consider arthroplasty, a surgical procedure to which the present invention is particularly applicable. Total joint arthroplasty or replacement is becoming an increasingly necessary surgical procedure as the population shifts to include a greater fraction of elderly and injured populations. Such a procedure often allows a patient to function and ambulate normally. In the recent past, orthopaedic surgeons have successfully implanted cemented total joint systems into patients. Although these systems have proven generally successful over long periods, surgeons are constantly attempting to increase the success rate of total joint arthroplasty.
Total joint replacement requires an involved surgical procedure conducted by a trained surgeon. Once the tissue surrounding the wounded joint has been temporarily removed, the surgeon begins preparing the intermedullary canal of a bone for the total joint arthroplasty. In the case of hip arthroplasty, the intermedullary canal of the femur is prepared in the following manner.
The proximal end of the femoral neck is first osteotomized. A gauge or osteotomy template is placed on the femur to provide the surgeon with a reference to decide where to sever the femoral neck. Once the femoral neck is removed, the femoral canal is exposed and is ready to be prepared to accept the femoral component of a total hip prosthesis. A few instruments are used in the procedure. These include a reamer, a broach, and optionally, a box chisel. All of these instruments are commonly known in the art of orthopaedic surgery.
A reamer is first positioned into the femoral intermedullary canal. While inserting the reamer, the surgeon rotates the reamer to sever the tissue and to enlarge the intermedullary canal. When the surgeon feels that enough tissue has severed, the surgeon removes the reamer from the femoral intermedullary canal.
A box chisel is next optionally employed. The box chisel is placed in the cavity created by the reamer. The box chisel is used to prepare the femur for improved broaching and to orient the broach for proper placement and anteversion. The box chisel prepares the opening of the cavity to comply with the cross-sectional geometry of a broach which is substantially rectangular in shape. A mallet or hammer is used to chisel the bone until the box chisel reaches the appropriate depth. The box chisel is then removed.
A broaching instrument, or simply called a broach, is next inserted into the intermedullary canal to create a cavity compatible with the prosthesis geometry. The surgeon must take care to insert the length of the broach along the same axis as was formed by the reamer. The surgeon impacts the protruding surface of the broach with a mallet or slide hammer until the collar of the broach is properly seated on the severed femoral neck surface.
A provisional neck is next placed in the broach to achieve proper neck length of the prosthesis. The provisional neck is adjusted until proper reduction is achieved to allow for proper range of motion in the joint. The provisional neck is then detached and the broach is removed from the intermedullary canal.
Finally, after the preceding preparation is complete, the femur is now ready to accept the femoral stem of a hip prosthesis. The femoral stem is cemented or press-fit into place and is now ready to accept the ball portion of the joint.
In the past, surgeons have employed a flexible wire in the above-described procedure. The wire was inserted into the length of the bone before reaming. The wire served as a guide over which a flexible reamer having a longitudinal bore therein was telescopically placed. Since the wire was flexible, it did not successfully serve as a guide for intermedullary canal preparation because the guide was not stationary. Instruments placed along or over the wire were free to move within the canal as freely as if no guide wire existed. Only flexible instrumentation was used in the prior art procedures which limited the surgeon's ability to effectively prepare the bone for accepting a prosthesis. The bores in the instruments were very small in diameter since the bores only had to fit over a wire having a diameter of up to about 1 millimeter.
When preparing a bone for a prosthesis, surgeons have consistently been met with the problem of locating the central axis of a bone. Location of the central axis of the bone is critical for a successful operation. If the prosthesis is not centered, uneven weight distribution causes problems both with respect to the bone and the prosthesis. Since the entire bone is not exposed during total arthroplasty, the surgeon has only a limited view of a portion of the bone. Therefore, locating the bone's axis is exceedingly difficult. To date, orthopaedic surgeons have not had reliable methods of successfully or accurately locating a bone's central axis.
The above-described procedure is met with other difficulties. If the surgeon does not insert the broach into the same cavity that the reamer was placed, the surgeon may easily crack the patient's bone. This results in prolonged surgery and prolonged healing time. The surgeon must also take care not to create an area which is exceedingly large and therefore is not suited to receive a prosthesis.
Clearly, such a complex surgical procedure would benefit from improved instrumentation.